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Study of anomalously high formation pressure of the Beshkent trough of the Bukhara-Khiva oil and gas bearing region
Изучение аномально высоких пластовых давлений Бешкентского прогиба Бухаро-Хивинского нефтегазоносного региона
- Institute of Geology and Exploration of Oil and Gas Fields (IGIRNIGM), Tashkent, Uzbekistan
Highlights
- Pressure-anomaly coefficient in the Beshkent trough: 0.96 to 2.
- Upper and Middle Jurassic carbonates, 87 objects: formation pressure 290.5–638.5 atm; porosity 5.4–12.15%.
- Salt–anhydrite formation 55–992 m thick at these objects; about 1,000 m in the depression zone of the trough.
- Correlation coefficients with salt–anhydrite thickness: above 0.74 for formation pressure and porosity; about 0.7 for the anomaly coefficient.
- Correlation coefficient between porosity and the anomaly coefficient: −0.705.
- Anomaly coefficient by facies: about 0.96–1.1 in the lagoon facies, 1.15–1.3 in the reef facies, 1.35–1.85 in the depression facies.
Abstract
Hypotheses explaining the possibility of abnormally high reservoir pressure are considered. The geological features of the Beshkent trough associated with the occurrence of zones of abnormally high formation pressures have been studied. The permeability-permeability, stress and geological parameters of the study area are analyzed. An analysis of factors affecting pore pressure and porosity is presented. The relationship between the coefficient of reservoir pressure anomaly and porosity for the Upper and Middle Jurassic carbonate rocks is determined.
English abstract from the journal issue PDF. The authors’ abstract, reproduced under .
In plain English
Written for oil and gas, this paper studies abnormally high formation pressure in the Beshkent trough of the Bukhara–Khiva region. Such pressure is found throughout the trough’s fields and prospects, with a pressure-anomaly coefficient of 0.96 to 2. Zones of abnormally high pressure are a frequent cause of accidents in deep drilling.
In the south-western spurs of the Gissar range and on the Chardzhou step there is a thick Jurassic complex of alternating salt and anhydrite layers. This salt–anhydrite formation is a seal that isolates oil and gas pools hydrodynamically. The authors compared formation pressure, porosity and the thickness of the salt–anhydrite formation at 87 objects in the Upper and Middle Jurassic carbonates of the Beshkent trough. Pressure ranges from 290.5 to 638.5 atm, porosity from 5.4 to 12.15%, and the salt–anhydrite formation is 55 to 992 m thick.
Pressure and the anomaly coefficient rise, and porosity falls, as the salt–anhydrite formation thickens: the correlation coefficient is above 0.74 for pressure and porosity and about 0.7 for the anomaly coefficient. Porosity also falls as the anomaly coefficient rises (correlation coefficient −0.705); the authors link this to clay in the reservoirs and to secondary changes such as calcite redeposition and dolomitisation. The salt–anhydrite formation thickens from north-west to south-east, to about 1,000 m in the depression zone of the trough. The anomaly coefficient follows the three facies zones: about 0.96–1.1 in the lagoon facies, 1.15–1.3 in the reef facies and 1.35–1.85 in the depression facies.
The authors conclude that the salt–anhydrite formation is the main regional control on abnormally high pressure in the trough’s carbonates. Overpressure accounts for variations in porosity, is a source of the reservoir energy that drives fluid flow, and may affect the productivity of the beds. Because the elastic properties of the rocks depend on it, the authors suggest that formation pressure between wells could be predicted from seismic data.
How to cite
O. A. Karshiev and K. M. Tokareva (2023). Study of anomalously high formation pressure of the Beshkent trough of the Bukhara-Khiva oil and gas bearing region. Geologiya i mineral'nye resursy (Geology and Mineral Resources), No. 2, 2023, pp. 58–60. https://mridm.uz/en/assets/journal/pdf/2_2023.pdf